Control of selective catalytic reduction (SCR) catalysts is of increasing interest to meet modern internal combustion engine emissions standards. The effectiveness of a typical SCR catalyst in removing oxides of nitrogen (NOx) emissions is sensitive to the temperature of the exhaust gas at the inlet to the SCR catalyst. Current catalyst formulations typically operate at peak efficiency when subjected to exhaust gas temperatures of 200-400° C. For certification of certain diesel engines, the emissions performance of the engine during the cold portion of the certification cycle is weighted almost equally with the emissions performance of the engine during the hot portion of the certification cycle. For this reason, improvements in preventing hydrocarbon (HC) and NOx emissions produced by the engine from slipping through the aftertreatment system at low temperature exhaust conditions, such as at temperatures less than about 200° C., as well as high temperature conditions, such as those in excess of 400° C., are desired.
Typical diesel A/T systems include a diesel oxidation catalyst (DOC) and a diesel particulate filter (DPF) in addition to the SCR catalyst. The DOC is responsible for oxidation of hydrocarbons (HC), carbon monoxide (CO), and nitric oxide (NO). Similar to the SCR catalyst, the DOC is not able to effectively and efficiently oxidize these molecules at cold exhaust temperatures. Furthermore, regeneration of aftertreatment components and the high temperatures associated with the same increases the consumption of reductant. Improvements in aftertreatment designs are required to mitigate the slip of these criteria pollutants through the exhaust flowpath during low temperature and high temperature operations and to reduce reductant consumption. Accordingly, further technological developments in this area are desirable.